1. Field of the Invention
The present invention relates generally to a dual purpose blow out preventer (“BOP”). Specifically, the BOP combines the functions of a deployment BOP with a typical wellhead pressure containment BOP. The invention is particularly useful in oil and gas well applications using a coiled tubing (“CT”) string connected to a bottom hole assembly (“BHA”) using a universal connect/disconnect (“UCD”). The invention may also be used in applications where mechanically actuated connectors are used to connect a BHA to a CT string.
2. Description of the Related Art
U.S. Pat. No. 6,209,652 (“the '652 patent”), incorporated herein in its entirety, discloses a deployment BOP for running tools into a well. The deployment BOP may be a 7 1/16 10,000 PSI BOP commercially offered by Vanoil Equipment Inc. of Leduc, Alberta, Canada. The deployment BOP provides at least two rams having sealing surfaces with a chamber defined between the sealing surfaces of the rams. The chamber has a port for communicating fluid to pressurize the chamber. A vertical position element is attached to the deployment BOP and a slip is also attached to the deployment BOP. Preferably, the vertical positioning element and the slip are associated with rams located within the BOP. A gate valve may be attached to the top of the deployment BOP and a wellhead pressure containment BOP attached to the bottom of the deployment BOP. A riser, either wireline or coiled tubing, is typically attached to the top of the gate valve depending on the desired operation. In a preferred embodiment, the deployment BOP has three rams with the lower ram having a slip and a sealing surface located above the slip. The middle ram also includes a sealing surface. The upper ram includes the vertical positioning element and the horizontal position adjusting element.
The '652 patent also includes a method for deploying tools in a live well comprising the steps of externally pressuring at least a portion of a first section of a connector tool in a pressure chamber at the surface of the well, the step of mating a second section of the connector tool with the first section longitudinally and the step of releasing the external pressure. The external pressuring step overcomes a force biasing a latch element of the first section. The pressure releasing step causes the latch element to longitudinally latch the second section with the first section. The method preferably includes rotationally aligning the first and second sections after longitudinally mating the sections.
Prior to the '652 patent, deployment systems often required rotational alignment of the connector tool sections before or during the connection of the sections. Rotational alignment of a CT string is not easy as neither half of the connector can be easily rotated. Further, the need for rotational alignment slowed down the process and required personnel around the riser during the process, a situation to be minimized in sour well operations. To solve this problem, the '652 patent discloses a novel UCD that is initially left free to rotate during the vertical connection and a rotational lock is triggered subsequently when the tool first experiences a rotational force. The system of the '652 patent uses pressure activation for implementing the release mechanism of the UCD. The system uses a piston designed to move at a predetermined pressure, affording release of the connector sections, thus providing for “hands-free” deployment.
The '652 patent discloses the method of making up a tool lowered within a BOP stack as follows. The lowest modular tool portion, having a lower section of a UCD affixed to its top, is made up with the upper section of a UCD connected to a wireline. The modular tool, and wireline are then pulled into the wireline riser and the wireline riser is raised and installed over the gate valve. The gate valve is opened and the modular tool section is lowered via the wireline through the deployment apparatus and coiled tubing BOP.
The tool is lowered below the upper vertical locating ram of the deployment BOP and the upper vertical locating ram is closed. The tool is then pulled up until a shoulder of the lower UCD section attached to the tool rests against a shoulder of the vertically locating deployment ram. The lower sealing slip ram and upper sealing ram are then closed about the lower UCD section. The closure of the lower sealing slip ram and upper sealing ram creates a sealed annular chamber around the UCD. The slip ram also supports the weight of the tool and pressure induced forces on the tool.
Fluid is applied to an annular chamber through a valve creating pressure in the chamber. The vertical connection between the lower UCD section attached to the tool module and the upper UCD section attached to the wireline is broken by means of the pressure. The wireline with its attached upper UCD section is raised into the wireline riser. The gate valve on top of the deployment BOP is closed.
The wireline riser is disconnected from the gate valve and returned to pick up a second tool module. Once a second tool module is loaded into the wireline riser, it is again reinstalled on top of the gate valve. This time the riser contains the wireline with its attached upper UCD section mated to a lower UCD section attached to the top of the second modular tool unit of the BHA. The second modular BHA unit is attached, as discussed above, at its bottom to an upper UCD section. Upon mating of the riser with the gate valve, the gate valve is opened and the second modular tool unit is lowered. The second unit with its upper UCD section attached to its bottom portion is lowered to rest upon a shoulder of the lower UCD section attached to the upper portion of the initial tool module, the lower section being held in the slip and sealing rams.
When the upper and lower UCD sections are vertically aligned and mated, the pressure is bled off in the annular chamber. When the pressure is released the UCD mechanisms lock together the upper and lower UCD sections. The union is, at this point, independent of the angular rotation of either UCD section, since the detent of the bottom section is circular. The deployment apparatus rams are now released and the first and second tool modules are lowered such that the lower UCD section attached to the top of the second tool module is in the deployment apparatus. The vertical locating ram is closed, and the lower tool section is pulled upwardly until its vertical height is adjusted. The sealing and slip rams are now closed around portions of the lower UCD section. Pressure is applied, as above, to disconnect the upper UCD section connected to the wireline from the lower UCD section affixed to the top of the tool string. The wireline and upper UCD section are pulled into the wireline riser, and the gate valve is shut.
The wireline riser is unmated from the gate valve and returned to the ground to pick up a third tool module, it also having a lower UCD section affixed to its top and an upper UCD section affixed to its bottom. The procedure is continued until the time comes to connect the upper tool module to the coiled tubing. At this point the coiled tubing riser, usually only a few feet long, is deployed in place of the wireline riser. The procedure to affix the last tool module to the coiled tubing head is similar to the above, the bottom end of the coiled tubing being connected to an upper UCD section. The coiled tubing riser will remain mated with the gate valve during tool operation downhole.
The deployment BOP disclosed in the '652 patent is very useful in the insertion of tools and a CT string into a well. However, as the '652 patent recognizes, such a “deployment BOP” does not perform a standard BOP function and is actually expected to be used in combination with a wellhead pressure containment BOP. One reason that a wellhead pressure containment BOP must be used in conjunction with the deployment BOP is the different functions of the rams in each BOP. Specifically, the rams in the deployment BOP are for the deployment of tool segments whereas the rams in a wellhead pressure containment BOP provide barriers to wellhead fluids at pressure. However, a wellhead pressure containment BOP and a deployment BOP both have slip and seal functions, but the rams in the deployment BOP typically seal on a BHA or UCD while the rams in a wellhead pressure containment BOP typically seal on the CT string. Usually the outer diameter of the BHA and UCD are larger than the outer diameter of typical CT strings. Thus, the different functions of the rams as well as the different outer diameters necessitate the use of two separate BOPs.
The use of a deployment BOP and a wellhead pressure containment BOP increases the overall height of the BOP stack. The increased height of the BOP stack increases the safety risk to those providing service and maintenance on the BOP stack. Further, the use of both a deployment BOP and a wellhead pressure containment BOP increases the capital and maintenance costs. The increased number of hydraulic rams also requires more accumulators and hydraulic circuits requiring more auxiliary equipment to run the BOP stack. Overall, the use of a deployment BOP in addition to a wellhead pressure containment BOP increases the costs expended on the operation.
However as noted above, a deployment BOP can be very useful in making up and breaking apart downhole tools. The purpose of the deployment BOP is to simplify the rig up and surface equipment when running long BHAs into a live well. Without a deployment system the entire BHA length must be accommodated in the CT riser. Therefore, the CT riser needs to be longer than the BHA's overall length. Because of the length of the CT riser, the injector must be located very high off the ground requiring a very large crane. Large cranes are expensive and working with heavy suspended loads is slow and less safe than handling smaller lighter loads. The deployment BOP permits running the tool into the live well in modules. Thus, the injector does not have to be as high of the ground. In addition, a wireline riser can be used to place the modules into the well. A wireline riser is much lighter than a CT riser and injector assembly, and even a long wireline riser can be managed with a relatively small crane. Further, it is often difficult to connect a CT string to a BHA located in the wellhead. This is due to the residual curvature of the CT string as it exits the CT injector into the BOP. As the CT string exits the injector the angle of the CT string may continue to change causing the end of the string to move to different radial locations within the BOP bore.
A BOP that functions as both a deployment BOP and as a wellhead pressure containment BOP may minimize the overall height of the BOP stack. Further, such a dual purpose BOP may allow the use of BHA modules such that a wireline riser may be used to run the BHA rules into the BOP. However, a BOP that performs these two functions may require bi-directional sealing rams. U.S. Pat. No. 6,877,712 to Wiedemann (“the '712 patent”), incorporated herein in its entirety, discloses a BOP having a set of rams that may seal bi-directionally.
The disclosed rams include an upper sealing surface, a lower sealing surface, an upper sealing element, an intermediate sealing element, and a lower sealing element. When the rams are containing pressure from below the upper sealing elements and the intermediate sealing elements contain the pressure. Likewise, when the rams are containing pressure from above the lower sealing elements and the intermediate sealing elements contain the pressure.
The '712 patent also discloses a first pressure diversion port and a second pressure diversion port. When the rams are in a closed pressure containment position the first pressure diversion port may divert pressure from below the set of rams to a chamber behind the rams. The second pressure diversion port may be used to divert pressure from above the set of rams to a chamber behind the rams. The diverted pressure may help to maintain the rams in a sealing position whether the pressure is diverted from above or below the rams. The '712 patent further discloses that a first valve may be used to selectively open or close the first diversion port and a second valve may be used to selectively open or close the second diversion port. The operation of such valves may be dangerous due to the high pressures often contained by a wellhead pressure containment BOP.
In light of the foregoing, it would be desirable to provide a BOP that minimizes the overall height of the BOP stack. Further, it would be desirable to provide a single BOP that functions as both a deployment BOP as well as a wellhead pressure containment BOP. It would also be desirable to provide a BOP that provides for the proper alignment of a CT string to be connect to a BHA. It would be desirable to reduce the number of rams used in a BOP stack by using rams that have both wellhead pressure containment and deployment functions. It would be desirable to design a BHA that can be deployed with the rams suitable for a CT string. Additionally, it would be desirable to remove the gate valve to further reduce the stack height and include its function into the BOP.
It would also be desirable to provide a bi-directional sealing set of rams that may be used in a dual purpose BOP. It would further be desirable to provide a valve that may be remotely actuated to allow pressure from above or below the set of rams to enter into a chamber behind the rams, the pressure helping maintain the set of rams in a sealing position. The remote actuation of the valve may minimize or eliminate the need to have personnel in the vicinity of the BOP. It may also be desirable to configure the pressure valves such that the valves failsafe to the wellhead pressure containment function.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.